Fitting the extra cooler will (if correctly mounted) increase the cooling efficiency and also increase the oil capacity. I don't think running too cool is likely to be a problem unless you are planning a winter trip to Norway!
(I suppose if you were concerned you could always plumb in a bypass line).
However it is worth thinking about the siting of the additional cooler; is it reducing the airflow over the engine or even the rectifier? If so you might lose some or all of the potential advantages.
Have found my 944 runs significantly cooler but so far with no sign of the oil emulsifying.
A.